Red cell sickling and neutrophil function. Hydrostatic pressure reversibly melts and inhibits the gelation of deoxygenated sickle hemoglobin gel. At 20 degrees C, a volume of activation for gelation of 70 cc mole-1 was found from the pressure induced increase in delay time. The increase in solubility of HbS was found to be at least 8.6 x 10-6 molar/PSI. The influence of piracetam (2-oxo 1 pirolidine acetamide) on the reduction of nitro-blue tetrazolium by human neutrophils was studied. Reduction was more rapid in the presence of piracetam, which suggests that piracetam enhances the production of superoxide by the neutrophil.